Isolated single transistor forward converters include apparatus for demagnetizing the isolation transformer during each cycle of operation. This demagnetization requirement is unique to this type of converter. Protection networks, or snubbers, are also required to keep the converter's switching transistor within its safe operating area.
Various demagnetizing arrangements have been utilized by others. One approach is referred to as a lossless demagnetizing circuit since the stored energy of the transformer is returned to the power source during each switching cycle. Although the stored energy is not wasted in heat loss with the arrangement, the transistor is required to switch the sum of the output power and the displaced power during each switching cycle. Another approach is to convert the stored energy of the transformer to heat energy by means of a zener diode connected across the primary winding. A third approach is to direct the stored energy of the transformer to an auxiliary output. This auxiliary output performs the demagnetizing function since it is connected to a load.
Similarly, various snubber networks have also been utilized. With the lossless snubber network, the stored energy of a snubber capacitor is returned to the power source during each cycle, but the switching transistor is again required to switch the sum of the output power and the displaced power during each cycle. Another approach is to convert the stored energy of the snubber capacitor to heat energy.